Retired chicken farmer Mihail Mihaisidis wanted a retaining wall.
Just a simple landscaping job in Kincumber, Australia.
He bought a sandstone block from a local quarry. Prepared to cut it. Prepared to stack it.
Then he flipped the stone over.
And his plans dissolved.
Right there in the rock lay the unmistakable print of an ancient animal. It wasn’t some trick of the light or a weird mineral vein.
It had a spine. It had limbs. It looked exactly like something that once swam.
“Even a non-expert can see it’s not just a pattern.”
For decades, this weird stone sat in storage at the Australian Museum after the family donated it. It languished in the dark, unnamed, just taking up space.
Then 2023 happened.
Scientists finally got around to describing the beast. They called it Arenaerpeton supin.
It’s an extinct amphibian relative. Specifically a temnospondyl.
Think of it like a prehistoric salamander. But make it chunkier. And nastier.
Lachlan Hart, a paleontologist from UNSW and the Australian Museum, pointed out the similarities to the modern Chinese Giant Salamander.
Superficially.
The head shape matches. But look closer. The ribs are huge. The soft tissue outline shows a heavyset body, not sleek like today’s descendants.
And the teeth.
Gnarly.
It had fang-like tusks on the roooftop of its mouth. Scary stuff.
Sandstone Usually Eats Fossils
Here is why this find is insane.
Fossils in sandstone are rare. Actually complete ones? Nearly impossible.
Sandstone forms in dynamic environments. High oxygen.
High oxygen means decomposition.
Usually, bodies break apart before they can be buried. Scavengers tear them up.
So you end up with a single tooth. Maybe an isolated bone fragment. Tracks.
Not a skeleton.
Not soft tissue.
Arenaerpeton is the only known specimen of its kind. It is fully articulated.
Head still attached to the body.
Skin impressions preserved in the rock matrix.
Matthew McCurry, also from UNSW and the Museum, called it one of the most significant fossils from New South Wales in thirty years.
“Key part of Australia’s fossil heritage,” he said.
He’s not wrong.
The researchers have a theory on how it survived.
Calm water.
Cold or anoxic bottom currents. No scavengers could handle those conditions.
The carcass sat undisturbed.
Decay slowed down. To a crawl.
The sediment sealed the shape before it could rot away.
Hart noted they don’t often find head-to-tail connections. And soft tissue? Even rarer.
Life in the Sydney Basin Before Dinosaurs
This thing lived 240 million years ago.
The Triassic period.
The Earth was just starting to breathe again after the “Great Dying,” the worst extinction event ever recorded. Dinosaurs hadn’t taken over yet.
Australia wasn’t a continent then. It was stuck to the Gondwana supercontinent, chilling near the South Pole.
Arenaerpeton swam the freshwater rivers of what is now the Sydney Basin.
It hunted fish. With its tusks.
We don’t have its tail.
But Hart estimates the full animal was about 1.2 meters long. Nearly 4 feet.
Big for an early Australian temnospondyl. But small compared to the giants that came later.
Does size matter in evolution?
Hart thinks so.
The last of these guys disappeared from Australia 120 million years later. And by then? They were massive.
The group survived two mass extinction events.
Maybe getting big was the survival strategy.
Maybe staying small kept Arenaerpeton around for its moment.
Or maybe it’s just a mystery we still haven’t solved.
It sat in a shed for years before becoming a star.
A literal hidden gem.
So next time you are buying rocks for your garden?
Flip it over first. 👀
